Imaging of solids

Hafner S, Demco D E and Kimmich R 1996 Magic echoes and NMR imaging of solids Solid State Nucl. Magn. Reson. 6 275-93... 

Marks L D and Smith D J 1985 Direot atomio imaging of solid surfaoes IV. Dislooations on Au(IOO) Surf. Sci. 157 L367... 

As has been shown in Section 5.4.3.3, imaging of solids can provide useful structural information about reactors, catalyst beds and so forth, and thus can be... 

LEED requires a coherence length of ordered domains on the order of at least 100 A to be useful (36). SEM images are typically limited to resolution of 50 A, but are useful due to their depth of field and wide field of view (37). High resolution TEM can yield images of solids to a resolution of 1-2 A, but requires extensive sample preparation and also requires that the surface atoms be in registry with the remainder of the bulk sample under study (14,38). Clearly, each technique provides valuable information which complements the others, and ideally a combination of the probes would be used to obtain a complete characterization of the surface under study. 

The most recent results of applying in situ STM/AFM to studies of corrosion convincingly demonstrate that novel and interesting images of solid-interface processes can be obtained. In fact, the images may be collected and presented consecutively, thereby enabling the viewer to follow the corrosion process as a moving picture in real time. In combination with simultaneous acquisition of electrochemical data, such as current-potential curves, these techniques provide excellent tools for... 

Atomic Force Microscopy (AFM). The AFM provides quantitative morpholographic images of solid surfaces at a nanometer scale. It uses a sharp tip scanned over the sample surface to sense attractive or repulsive forces between the tip and the surface. The microscopic image of the surface is obtained as a surface, representing the locus of points of constant force between the tip and the sample. 

Dubes, A., et al.. Scanning electron microscopy and atomic force microscopy imaging of solid lipid nanoparticles derived from amphiphihc cyclodextrins. Eur. J. Pharm. Biopharm., 55, 279-82, 2003. 

NMR imaging of solids is a technique that can be divided into two areas, depending upon the characteristics of the sample (7-6). For "soft" solids, the presence of local, rapid molecular motions reduces homonuclear dipolar coupling and averages anisotropic chemical shielding. Thus, the natural line width is narrow (long T2) and it is relatively easy to encode spatial information with a magnetic field... 

Recently a whole new family of microscopic techniques has been invented which enable the in situ imaging of solid surfaces using local probes. By local we mean that resolution can approach atomic dimensions, implying that probe size and accuracy of controlling its movement over the surface limit the resolution. The probe is usually located at atomic distances from the sample and is not influenced by the medium. 

As a final example, we mention the combination of solid-state spectroscopy (Chapter 15) with imaging. The imaging of solids is difficult because the 7Ys are often too short compared with the time it takes to switch and apply field gradients for slice selection and phase and frequency encoding, while in addition extremely large gradient amplitudes are required to overcome the broad line widths. The time to ramp... 

Contact AFM [241, 242] Topographic imaging of solid substrates Mechanical properties Local adhesive properties... 

In combination with multi-pulse excitation, rotating-frame imaging can also be used for imaging of solids [Choi]. A time-suspension multi-pulse sequence (cf. Table 3.1) is applied to the sample by use of an rf coil with a homogeneous B field so that both... 

Fig. 8.5.3 Proton MAS images of solid discs (750 iJtm thick and 3.5 mm diameter) of poly(butadiene)-poly(styrene) blends, (a) Mechanical blend of both components, (b) Blend cast from solution in toluene. The image contrast is caused by the differences in the strengths of the dipole-dipole couplings among H for the two polymers. The signals from poly(styrene) are filtered out (white) so only poly(butadiene) protons contribute to the image (dark). The spatial resolution is better than 50 p-m at a spinning frequency of 5 kHz. Adapted from [Cor4]. Copyright 1989 American Chemical Society.

Many methods for improvements of the spatial resolution in NMR imaging of solid materials have been proposed with different impact on applications in polymer science [8, 9, 11-13, 21]. For the great variety of techniques only those are reviewed in Sections 5.1.3 and 5.1.4 below, which are being applied successfully to problems in polymer science. Depending on the dominating features, the techniques can be classified into frequency and phase encoding approaches. 

A simple but often very successful approach in imaging of solid materials is the use of liquids as contrast agents, because they can be investigated by standard techniques. Porous structures like foams, internal cracks, voids or other spatial features can easily be analyzed in this way [116]. Furthermore, the local separation of liquids in pastes depending on external forces has been demonstrated in extrusion processes of PTFE/water pastes [94]. This kind of investigation is based on the assumption that the interaction of the... 

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